Telephone line pairs can have faults caused by any number of factors. A line fault can result from repair or construction around the lines such that a line pair is broken or shorted together. These types of faults are readily identifiable and rarely is any form of test equipment required to locate the fault.
More elusive faults are caused by improper splices causing a condition known as a "split," or by improperly terminating a line pair. A fault can also result from natural influences such as moisture seeping into the line pair causing corrosion, rodents chewing through the line pair, or lightning strikes on the cable. Test equipment is needed for detecting these line pair faults.
Typically a craftsperson is sent into the field to analyze faulty telephone line pairs. The system test equipment used is often bulky and difficult to handle by a typical craftsperson. The usefulness of such test equipment is further limited because only one test function out of many essential fault analysis or location techniques is available in a single piece of test equipment. Therefore, to effectively troubleshoot a line pair, the craftsperson must bring with him a miscellaneous collection of diagnostic equipment.
Compounding an already onerous task, each piece of test equipment is functionally different and has its own nuances. The craftsperson must intimately know the intricacies of each piece to effectively troubleshoot the line pair in the field. A large learning curve and years of experience are required to adequately train craftspersons before they become sufficiently familiar with each piece equipment.
When analyzing a line pair a craftsperson verifies whether the line pair's characteristics of capacitance, resistance, and voltage parameters are within industry standards. A line pair has a tip leg, a ring leg and a ground leg. The capacitance parameters comprise those capacitance values from ring-to-tip, ring-to-ground and tip-to-ground, or C.sub.RT, C.sub.RG and C.sub.TG, respectively. A line pair's capacitance value is largely a function of the dielectric used and the amount of twist in the line pair. A line pair's resistance values, R.sub.TIP, R.sub.RING and R.sub.GND, respectively, are functions of wire gauge. That is, the lower the wire gauge, the greater the thickness of the wire, and therefore the lower the resistance.
Prior meters typically implement a one-dimensional analysis which merely measures the resistance of the line pair using a direct current ("DC") method or simply measure the capacitance of the line pair using an alternating current ("AC") method using a time domain analysis based on Laplace transforms. A barrier to effective use of the DC method is the presence of series capacitance effects between the legs of a line pair. Because the capacitance acts as a DC filter, conventional meters cannot detect a series resistance fault caused by, for example, a bad connector. Thus, another piece of test equipment would have to be used to fully diagnose the line pair. More often than not, the craftsperson would have to terminate the opposite end of the line pair to perform these additional tests, requiring the craftsperson to travel to the far end of the line pair and to travel back to complete the tests.
Some test equipment provides longitudinal balance tests that allow single-ended testing to verify that the tip and ring legs of the line pair are "equal" and therefore are balanced. Such a test can alert the existence of a fault to a craftsperson but cannot describe the type or location of the fault.
Examples of test equipment used to locate line pair faults and splits are the "Cable Fault Locator," model number C-4904A and the "Open and Split Fault Locator" model number C-4910G, both available from Communications Technology Corporation.
The "Cable Fault Locator" is a cable fault locator system which locates grounds, shorts, crosses and splits. The system determines the path and depth of a buried line pair or cable by transmitting a high energy tone onto the telephone line pair to induce an electromagnetic field. The craftsperson must walk the length of the line pair with an inductive wand to detect the electromagnetic field propagating from the buried line pair. While walking, the craftsperson monitors an analog meter for indications of where the fault may be. The craftsperson may have to walk anywhere from 10 feet to 40,000 feet before locating the fault.
The "Open and Split Fault Locator" provides a digital meter readout for determining the location of a split in a spliced line pair. To operate the device, a craftsperson first must determine which line pairs comprise the split and then ensure that the line pairs being tested are of equal length else the test cannot produce an accurate split location. Such "open and split locator" devices utilize two-terminal capacitance measurement methods which cannot distinguish the individual C.sub.TR, C.sub.TG and C.sub.RG capacitances affected by the presence of a split. Typically, the C.sub.TG capacitance of the analyzed line pair decreases in magnitude and the line pair C.sub.RG and C.sub.TG capacitances increase in magnitude.
When devices such as the "cable fault locator" and the "open and split fault locator" cannot accomplish the desired objectives, the craftsperson resorts to an analog meter commonly referred to as a "kick meter." The term "kick meter" describes the action of the meter needle when the meter is initially attached to a line pair. The needle "kicks" across the meter in proportion to the amount of capacitance present on the line pair up to a parallel fault. The craftsperson, based on his experience, guesses the distance along the line pair to the fault. The accuracy of the craftsperson's guess is further cast into doubt if there is a resistance in the line, such as a series fault. The presence of a series fault affects the "kick" of the needle and therefore affects the craftsperson's guess as to where the fault is located.
Advancements in measuring techniques brought into use three-terminal measurement analysis where the tip, ring and ground legs are connected for a three-terminal analysis. Although an advancement from commonplace two-terminal measurements, the devices implementing three-terminal measurement analysis also have downfalls. First, these devices operate using waveforms having only one frequency, allowing only a one-dimensional analysis. Second, these prior devices implement antiquated technology using synchronous detectors which rely heavily on electronic hardware, adding to the weight and the bulk of the unit. Furthermore, because of the reliance on hardware, numerous potentiometers are incorporated. The greater the number of potentiometers, the greater the device's complexity and the need to calibrate the unit before each use. Also, these prior devices cannot compensate for inductances in the line pair which would render the devices useless. A further limitation inherent with these prior devices is that only direct current (DC) resistances, or "zero-phase" impedances," are analyzed. Alternating current (AC) resistances are ignored except for determining whether "clipping" of test waveforms occurs in the line pair. Clipping affects the accuracy of a measurement obtained by these prior devices.
A need exists for a line pair analyzer which is compact, complete, lightweight and easily used by a craftsperson. Additionally, a need exits for devices providing exacting measurements in a minimal amount of time and training to allow a craftsperson to expeditiously obtain a complete line pair diagnostics.